This invention relates to oil-free poly(aryloxyphosphazene) copolymers. More particularly, this invention relates to poly(aryloxyphosphazene) copolymers containing residual amounts of P-Cl bonds which produce elastomeric characteristics in the copolymers even in the absence of relatively low molecular weight polyphosphazene oils which are normally required to impart such characteristics.
Various elastomeric poly(aryloxyphosphazene) polymers and copolymers have been previously described in the prior art. Thus, for example, U.S. Pat. Nos. 3,515,688, 3,856,713, 3,970,533 and Polymer 13,253 (1972) describe elastomeric polyphosphazene copolymers. However, these materials exhibit a number of disadvantages which materially reduce their usefulness. For example, many of the copolymers disclosed therein contain fluorinated substituents which make them expensive. In addition, the solubility of such copolymers is rather limited. Moreover, it has been found in many instances that the elastomeric properties of the copolymers are dependent on the existence in the copolymer of minor but significant proportions of low molecular weight phosphazene oils. Thus, for example, copending application Ser. No. 876,384, filed on Feb. 8, 1978, and commonly assigned, discloses that the presence of relatively low molecular weight phosphazene oils in poly(aryloxyphosphazene) polymers, either as a deliberate addition to the polymer or as retained during preparation, provides for elastomeric characteristics in the polymer while the absence of such oils results in a leathery, difficult to process material. In addition, U.S. Pat. No. 3,943,088, also commonly assigned, discloses that the physical properties, particularly stress/strain, elongation and low temperature flexibility, of poly(fluoroalkoxyphosphazenes) are dramatically improved by the addition of relatively low molecular weight phosphonitrilic fluoroalkoxides (oligomers or cyclics).
As disclosed in the aforementioned copending application and U.S. Pat. No. 3,943,088, the addition of such low molecular weight phosphazene oils to the polyphosphazene polymers described therein does result in significant improvements in the elastomeric characteristics of the polymer. However, such a method of providing elastomeric properties also involves significant disadvantages. Thus, as described in the copending application, the relatively low molecular weight phosphazene oils along with high molecular weight polydichlorophosphazenes are produced during the thermal polymerization of --(NPCl.sub.2).sub.n -- oligomers, where n = 3 to 9. Accordingly, where it is desired to add such oils as a separate addition product to a polyphosphazene polymer, particularly a polyphosphazene polymer which has been derivatized by methods such as are described in, for example, U.S. Pat. Nos. 3,370,020, 3,515,688, 3,700,629, 3,702,833, 3,853,794, and 3,972,841; it is first necessary to separate the low molecular weight oily material from the high molecular weight polydichlorophosphazene, and then add it to the derivatized polyphosphazene polymer. As will be evident, it is, of course, possible to retain the low molecular weight oily material along with the higher molecular weight polydichlorophosphazene and then derivatize the mixed materials. However, this results in the production of derivatized polymer having mixed structures which may adversely ffect the properties desired in the derivatized polymer.
In accordance with this invention, it has now been discovered that polyphosphazene copolymers having elastomeric characteristics can be prepared in the absence of relatively low molecular weight phosphazene oils, and without the aforementioned disadvantages by retaining some proportion of Cl in the form of P-Cl bonds (i.e. from about 0.4 to about 10 percent by weight based on the total weight of copolymer).